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I have a 2005 Toyota Tacoma PreRunner 4.0 V6, which has been the most reliable vehicle I’ve ever owned! Until recently..

It seems like everything started about a year or so ago. I was in my truck with it running in park, and I looked down and noticed my truck was pegged. There’s no telling how long it was running hot. I immediately turned it off, let it cool and topped off the antifreeze.

About two to three weeks later, it started skipping badly when going up hills. I cleaned the MAF Sensor and replaced all 6 of the Coil Packs, thinking this would help. It did okay for a while, but then I noticed I was needing to fill the coolant up every few days. I thought the head gasket was blown, and noticed water coming out of the tail pipe. I used Blue Devil, which seemed to fix it because it’s not leaking anymore and there’s no oil mixing with the coolant.

Replacing the coil packs seemed to fix the skipping and sputtering problem when accelerating up hills, somewhat.

Eventually, however, my truck has started to have an extremely rough idle. When cranking up the truck, it spits and sputters so badly it’ll stall out if I don’t rev up the engine right away. When I take off and drive a couple yards, it drives okay until it stops and idles. Then the process starts again. This happens more frequently and does it way worse when the weather is hot. When it’s cold outside, it may do it if driven for a while but no where near as badly.

Throughout this whole process, the check engine light has only gone off about two weeks when the coil packs were replaced, so it’s basically been on constantly.

I’ve replaced the crank shaft sensor and one of the cam shaft sensors (the driver’s side - which was the one throwing the code.) I’ve also replaced both upstream Air Fuel Ratio o2 Oxygen Sensors and the PCV Valve.

The truck is still throwing p0171 and p0174 and P0300 (see attached file for Live Data Sheet and attached images for up to date diagnostics scan)

I have no idea what could be the issue. I’ve taken it to several friends who work in the automotive industry, and have searched online hours upon hours to no avail. If you have any knowledge or advice about what this issue could be, I would VERY MUCH appreciate it!

Thank you in advance!!
 

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Mambeau / Admin
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Let's go back to the overheating incident ... How low on coolant were you? Did this happen while the outside temperature was hot?

Have you checked all the PCV and vacuum hose connections?

Have the timing, compression, and valve clearance been checked since all this started?

Have you confirmed your fuel pressure is within spec?

You didn't mention any checks made on the injectors. Have you verified all 6 injectors are un-fouled and working properly?

There are any of a number of electrical faults (shorts; bad connections) that could fake the ECM into running badly.
 
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Mambeau / Admin
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Those check engine codes, along with the rough idle make me think that MAF sensor is bad.
Good point ... Newby86 only mentioned cleaning it last year(?).
 

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I’d block tested before anything else. You need to find out why the coolant went low. Blue Devil, and stuff like that isn’t a repair. It usually used to get the vehicle home where it can be repaired properly. You also run the risk of restricting the thermostat or worse, the radiator.
 
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